This invention relates to an apparatus and a method for monitoring electrochemical cells. Specifically, the present invention deals with a combination of equipment to provide continuous, reliable and efficient monitoring of a selected electrochemical cell from a caustic-chlorine electrochemical multicell electrolyzer, either single or multicell. While multicell electrolyzers are well known and widely used in the caustic-chlorine production industry, see for example Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 1, John Wiley & Sons, Inc., N.Y., 1978, pp. 806-825, it is always desirable to provide a means and method to check the operation of the electrolyzer. Usually, this is done by checking the overall voltage on the electrolyzer and the caustic and chlorine make. While it is impractical to have every electrochemical cell of a multicell electrolyzer monitored, it is feasible to spot check a pre-selected electrochemical cell using a standard calomel reference electrode to measure the anode or cathode overvoltage, for example with a Luggin capillary probe, as is conventionally known. However, this involves connecting the selected electrochemical cell to a voltmeter and the voltmeter to a reference electrode which is in contact with the cell bath of the multicell electrolyzer. Such connections are required prior to beginning operations in a multicell electrolyzer, are used to monitor only one cell, and cannnot be changed during operation of the multicell electrolyzer. Unfortunately, such operation has suffered from leakage at various connections, attack on monitoring equipment from the cell bath, breakage of the glass Luggin capillary tubes, and pinching of the sample line from the cathode compartment to the reference electrode. Further, the probes themselves are relatively costly and difficult to reach for installation.
Another overvoltage measurement system is described in U.S. Pat. No. 4,163,698 to Kuo et al which teaches connecting an insulated platinized platinum or RuO.sub.2.TiO.sub.2 coated Ti wire tip from 0.2 to 1.0 millimeters away from the gas producing electrode in the gas stream produced and connected at the other end to a voltmeter and to the electrode itself, and then reading the overvoltage directly on the voltmeter. However, the reference electrode wire tip is exposed to a corrosive environment and quickly loses the sensitivity of its original state.
Hall et al., U.S. Pat. No. 3,291,714, teaches an electrode for an electrolytic cell which includes an iron support coated with an iron alloy of molybdenum or tungsten to overcome corrosion problems and in which the cell has a conventional glass Luggin capillary which penetrates a rectangular polyethylene washer, which is used to space apart the electrodes and diaphragm membranes. The Luggin capillary extends into the cell and is spaced slightly apart from the center of the cathode and connects to the reference electrode by a salt bridge. U.S. Pat. No.
3,077,446 to Van den Berg teaches a reference electrode for pH meters which includes a tubular vessel with a capillary opening at one end for flow of liquid, a reference electrode in the tubular vessel and an electrolyte liquid which in addition to the water and potassium chloride has a nonionizing soluble organic compound, such as a glycol or glycerol, to depress the freezing point of the electrolyte and in which the capillary tube is a flexible elongate conduit having a flow restricting rigid glass stopcock. Crippen et al., U.S. Pat. No. 3,871,985, teaches a tip block for the conventional Luggin capillary tube which is of plastic material such as polypropylene or Teflon, and has an L-shaped channel which carries and protects the Luggin tube tip from damage. None of the prior art references teach an unbreakable capillary tube which can be securely placed and retained its position adjacent the electrode selected for monitoring, or which are capable in practical operation of being placed at more than one position in a cell. According to the present apparatus, and the method for using it, a safe, reliable, functional and convenient monitor system for a selected electrochemical cell of a multicell electrolyzer having a common electrolyte is provided.